Chromium-Catalyzed Asymmetric Dearomatization-Addition Reactions of Halomethyloxazoles and Indoles

Article abstract of DOI:10.1055/s-0037-1609753

The asymmetric dearomatization-addition reaction of halomethyloxazoles and halomethylindoles with aldehydes is realized in the presence of a carbazole-based bisoxazoline CrCl ₂ complex to afford the corresponding enantioenriched, hydroxylated oxazoline and indoline products. The observed excellent chemo-, regio-, diastereo- and enantioselectivities are notable advantages of this protocol. The strategy established in this study is expected to find application in the synthesis of azaheterocycles with biological significance and useful functionalities.

Full text of DOI:10.1055/s-0037-1609753

SYNTHESIS
0
0
3
9
-
7
8
8
1
1
4
3
7
-
2
1
0
X
© Georg Thieme Verlag Stuttgart · New York
2018, 50, A–G
special topic
A
en
Z. Wang et al.
Special Topic
Synthesis
Chromium-Catalyzed Asymmetric Dearomatization–Addition
Reactions of Halomethyloxazoles and Indoles
Zheng Wanga
Hongtao Jia
Wei-Min He*a
Yang Xiongb
HO
X
R
OH
R
OH
O
RCHO
RCHO
0
0
0
0
0-
0
0
2
9-
4
8
1
6-
6
9
7
R1
CrCl2/L
CrCl2/L
N
N
N-
N
aromatic
R1
Ts
Ts
6 examples
Guozhu Zhang*b
0
0
0
0
0-
0
0
2
2-
2
2
2
6-
3
0
5
Me
9 examples
X = Br, Cl
1 example
up to 70% yield
dr up to 99:1
ee up to 95%
a Hunan Provincial Engineering Research Center for Ginkgo
biloba, Hunan University of Science and Engineering, 130
Yangzi Tan Road, Yongzhou 425100, P. R. of China
weiminhe2016@yeah.net
63% yield
dr 99:1
ee 90%
R1 = alkyl, aryl, alkenyl
up to 69% yield
dr up to 99:1
ee up to 95%
b State Key Laboratory of Organometallic Chemistry, Shanghai
Institute of Organic Chemistry, Center for Excellence in
Molecular Synthesis, Chinese Academy of Sciences,
345 Lingling Road, Shanghai 200032, P. R. of China
guozhuzhang@sioc.ac.cn
Published as part of the Special Topic Modern Dearomatization Strategies in Synthesis
Received: 06.02.2018
Accepted after revision: 09.04.2018
Published online: 29.05.2018
the most active and important topics in synthetic organic
chemistry. Among the methods established, the catalytic
asymmetric dearomatization (CADA) reaction of azahetero-
cycles has become a straightforward and powerful tool,[4]
allowing rapid access to advanced intermediates for the
synthesis of alkaloids in a highly diastereoselective and en-
antioselective manner. Quite a few azaheterocycles, includ-
ing indole and pyrrole, have been proved to be viable sub-
strates for CADA reactions.[5] However, the reported cou-
pling partners were mainly metal-activated allylic
electrophiles, giving allylative dearomatization products. As
one special type of arene, halomethyl azaheterocycles rep-
resent a class of important building blocks leading to al-
kylated products. Dearomatization-type reactions of ha-
lomethyl azaheterocycles have been scarcely investigated.[6]
To the best of our knowledge, the asymmetric version re-
mains an unmet challenge. Undoubtedly, new strategies to
address this issue would be synthetically useful and mecha-
nistically interesting, not only enriching the dearomatiza-
tion toolbox, but also offering a facile and potent entry to
enantioenriched azaheterocycles and their derivatives.
We recently reported the first asymmetric dearomatiza-
tion–addition reactions of halomethyl naphthalene and
heteroarenes (S, O) with a broad range of aldehydes under
chromium-catalyzed conditions, leading to highly function-
alized hydroxylated 1,2-dihydronaphthalenes or O- and S-
heterocycles.[7] In line with our continuing interest on
asymmetric chromium catalysis,[7–9] herein, we report our
preliminary results on the successful expansion of this nov-
el strategy to halomethyl azaheterocycles. A series of opti-
cally pure, highly functionalized oxazoline and indoline
products can be readily accessed under chromium-cata-
lyzed reaction conditions (Scheme 1).
DOI: 10.1055/s-0037-1609753; Art ID: ss-2018-c0070-st
Abstract The asymmetric dearomatization–addition reaction of halo-
methyloxazoles and halomethylindoles with aldehydes is realized in the
presence of a carbazole-based bisoxazoline CrCl2 complex to afford the
corresponding enantioenriched, hydroxylated oxazoline and indoline
products. The observed excellent chemo-, regio-, diastereo- and enan-
tioselectivities are notable advantages of this protocol. The strategy es-
tablished in this study is expected to find application in the synthesis of
azaheterocycles with biological significance and useful functionalities.
Key words asymmetric–dearomatization, chromium catalysis, oxazo-
lines, indolines, azaheterocycles
Nitrogen-containing heterocyclic compounds (azahetero-
cycles) are essential components in numerous natural prod-
ucts, potent pharmaceutical drugs, and various types of
functional materials. Although diverse synthetic approach-
es toward functionalization of azaheterocycles have been
described,[1] the development of versatile and flexible
methodologies for facile azaheterocycle derivatization with
selective control of substitution patterns are still highly de-
sirable.
Alkaloids and synthetic small molecules with an indo-
line or oxazoline structure exhibit a broad range of import-
ant biological activities and versatile functionalities, espe-
cially in chiral ligand development.[2] For the synthesis of
structurally diverse and complex oxazoline and indoline
derivatives, utilization of the embedded C–C double bonds
of oxazoles and indoles has high synthetic potential, since a
new covalent bond is formed in one step on the heterocycle
with high atom economy.[3] The development of efficient
methods for the synthesis of optically pure and highly func-
tionalized azaheterocyclic compounds constitutes one of
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2018, 50, A–G

B
Z. Wang et al.
Special Topic
Synthesis
HO
X
R
OH
OH
O
RCHO
RCHO
R1
CrCl2/L
CrCl2/L
N
N
R
N-
N
aromatic
R1
Ts
Ts
6 examples
Me
9 examples
X = Br, Cl
1 example
up to 70% yield
dr up to 99:1
ee up to 95%
63% yield
dr 99:1
ee 90%
R1 = alkyl, aryl, alkenyl
up to 69% yield
dr up to 99:1
ee up to 95%
Scheme 1 Reactions of halomethyl azaheterocycles
At the outset of this study, readily available 5-(bromo-
methyl)-2-phenyloxazole (2a) and 3-phenylpropanal (1a)
were selected as model substrates to examine this process.
The reaction conditions were adopted from our previous
studies [i.e., a catalytic amount of CrCl2 and ligand, Proton
Notably, in contrast to those adducts derived from the
1-(bromomethyl)naphthalene, which were prone to de-
compose under weak acidic environments, compound 3a
was relatively stable under normal storage conditions.[7b]
Relying on a single crystal X-ray analysis from a previous
study of the dearomatization of 2-(chloromethyl)benzo-
furan,[7a] and a proposed working transition model (Figure
2), the configuration of the product 3a (>95% ee) was tenta-
tively assigned to be R,R.
Sponge
(N1,N1,N8,N8-tetramethylnaphthalene-1,8-di-
amine) as the base, a stoichiometric amount of Mn as the
[11]
reductant,[10] ZrCp2Cl2
as the dissociating reagent]. The
screening of chiral ligands (Figure 1) for this asymmetric
dearomatization–addition reaction revealed that modified
Nakada ligand L4 was the optimum ligand among those ex-
amined.[7a,9e] We tested tetrahydrofuran, acetonitrile, and
1,2-dichloroethane as solvents and found that the use of
1,2-dichloroethane led to a better yield of the coupling
product. Lowering the temperature to –10 °C further im-
proved the reaction in terms of yield and ee. Notably, for all
HO
O
NCl
Cr
Me
N
R
N
N
O
N
O
Me
H
O
Ph
R
H
Ph
O
1
the reactions, only one diastereomer was detected by H
Figure 2 Proposed transition state
NMR spectroscopy. In addition, no benzylic adduct was ob-
served. The reaction scale could be increased to 0.5 mmol
with maintenance of the efficiency. Thus, the optimum
conditions were established to be those shown in Scheme
2.
With the optimized reaction conditions identified, the
couplings of several aldehydes with 5-(bromomethyl)-2-
phenyloxazoles were explored (Scheme 3). A terminal
chloro group was well tolerated under the standard condi-
tions, as 5-chloropentanal reacted to give the desired prod-
uct 3b in 61% yield and 94% ee. The reaction of the naturally
occurring aldehyde (±)-citronellal proceeded well, affording
product 3c in 51% yield and over 95% ee, suggesting that the
chiral β-methyl did not interfere with the enantioinduc-
tion. The effect of substituents on the phenyl ring of the ox-
azoles was then briefly investigated; to our delight, both
bromo and fluoro groups were well tolerated at para and
ortho positions, with the corresponding products 3d–i be-
L1: R = i-Pr
L2: R = Ph
L3: R = i-Bu
L4: R = Et
N
H
N
O
O
H
N
O
O
N
N
R
N
R
L5
Figure 1 Tested ligands
1) CrCl2 (10 mol%)
L4 (13 mol%)
Proton Sponge (13 mol%)
DME, r.t.
HO
O
Br
N
CHO
O
+
N
2) Mn (2 equiv)
ZrCp2Cl2 (1 equiv)
DME, –10 °C
1a
2a
3a
57% yield
99:1 dr
95% ee
Scheme 2 Optimized conditions for the CADA addition of 5-(bromomethyl)-2-phenyloxazole (2a) with 3-phenylpropanal (1a)
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2018, 50, A–G

C
Z. Wang et al.
Special Topic
Synthesis
ing obtained in good yields with excellent dr and ee values.
Aryl aldehydes and α,β-unsaturated aldehydes were also
examined, but after numerous trials, unfortunately, we
were unable to obtain sufficient amounts of products for
characterization due to contamination with significant
quantities of inseparable impurities.
hex-2-enal also reacted well, providing dearomatized prod-
ucts 4d and 4e in high enantiomeric excesses (95% and 93%
ee, respectively).
The effect of indole substituents was examined next. To
our delight, the phenyl ring of indole could be functional-
ized with a chloro group 4f, rendering this methodology
with added synthetic value. This dearomatization–addition
protocol could also be extended to 3-(bromomethyl)indole,
and the corresponding reaction with (E)-hex-2-enal pro-
ceeded smoothly to give product 4g in a useful yield and ex-
cellent diastereoselectivity, but with slightly decreased en-
antioselectivity.
1) CrCl2 (10 mol%)
L4 (13 mol%)
HO
R
Br
Proton Sponge (13 mol%)
DME, r.t.
N
O
N
R'
+
O
H
R
2) Mn (2 equiv)
ZrCp2Cl2 (1 equiv)
DME, –10 °C
R'
O
1
2
3
In summary, the first asymmetric dearomatization–ad-
dition reaction of readily available halomethyl azaheterocy-
cles, including oxazoles and indoles, with a variety of alde-
hydes was realized under chromium-catalyzed conditions,
leading to optically pure elaborated molecules with two ad-
jacent stereogenic centers. Given the high prevalence of
azaheterocycles in biologically active molecules and func-
tionalized materials, it is expected that this catalytic system
will find wide application for the synthesis of complex mol-
ecules with medicinal significance and beneficial uses.
Me
Cl
Me
HO
O
Me
HO
O
N
99:1 dr
94% ee
61% yield
N
1:1 dr
95% ee for each
diastereomer
51% yield
3b
3c
Cl
Me
HO
O
HO
N
N
99:1 dr
93% ee
45% yield
99:1 dr
95% ee
60% yield
O
N
3d
3e
Br
Br
All manipulations were carried out under argon using standard
Schlenk techniques. All glassware was oven- or flame-dried immedi-
ately prior to use. All solvents were purified and dried according to
standard methods prior to use, unless stated otherwise. All reagents
were obtained from commercial sources and were used without fur-
ther purification. Thin-layer chromatography (TLC) was performed
using Jiangyou, Yantai, China 60 mesh silica gel plates and samples
were visualized with short-wavelength UV light (254 nm, ZF-1,
Shanghai Gucun Optic Instrument Factory), silica gel 60 (200–300
mesh) was used for column chromatography. Optical rotations were
measured using a Perkin-Elmer 341 polarimeter. IR spectra were re-
corded on a Nicolet FT-IR spectrophotometer; only major peaks are
reported in cm–1. 1H and 13C NMR spectra were obtained at 400 MHz
and 100 MHz, respectively, using an Agilent (400 MHz), VARIAN (400
MHz) and Bruker (400 MHz) spectrometer. 1H NMR data are reported
relative to tetramethylsilane (0 ppm) or the residual protonated sol-
vent signal. 1H NMR data are recorded as follows: chemical shift (δ,
ppm), multiplicity (s = singlet, d = doublet, t = triplet, q = quartet, m =
multiplet or unresolved), coupling constant (J) in Hz, integration.
13C NMR chemical shifts are reported relative to the solvent resonance
(CDCl3, 77.16 ppm). High-resolution mass spectrometry (HRMS) was
performed using a EI-HR (GC-TOF) spectrometer. High-performance
liquid chromatography (HPLC) was carried out with an Agilent 1260
Infinity instrument employing a UV spectrophotometric detector
(210 nm, Agilent).
Me
Cl
HO
O
HO
O
94:6 dr
94% ee
65% yield
N
99:1 dr
94% ee
70% yield
3g
Br
Br
3f
Me
Me
HO
O
HO
N
N
94:6 dr
94% ee
57% yield
94:6 dr
94% ee
50% yield
O
3i
F
3h
Br
Scheme 3 Substrate scope studies
The generality of this strategy was further demonstrat-
ed by the utilization of chloromethyl indoles 5 as the sub-
strates (Scheme 4). The reaction conditions were slightly
modified with the addition of a catalytic amount of NiCl2
and one equivalent of CsI to obtain better results. In terms
of the scope of the aldehydes, aryl aldehydes performed
much better as coupling partners in this reaction. The
dearomatization–addition reactions of 2-(bromomethyl)-1-
tosyl-1H-indole with three representative aryl aldehydes,
including benzaldehyde, 3-fluorobenzaldehyde and 2-
methylbenzaldehyde, proceeded well to provide the highly
functionalized indoline derivatives 4a–c in moderate to
good yields and excellent stereoselectivities. α,β-Unsaturat-
ed aldehydes such as (E)-3-(o-tolyl)acrylaldehyde and (E)-
(R)-1-[(R)-5-Methylene-2-phenyl-4,5-dihydrooxazol-4-yl]-3-
phenylpropan-1-ol (3a); Typical Procedure
In a glovebox, to a mixture of anhydrous CrCl2 (1.2 mg, 0.01 mmol),
1,8-bis[(S)-4-ethyl-4,5-dihydrooxazol-2-yl]-9H-carbazole (L4) (4.6
mg, 0.013 mmol) and Proton Sponge (2.8 mg, 0.013 mmol) was added
DME (0.2 mL) under a nitrogen atmosphere. The mixture was stirred
vigorously at r.t. for 2 h before being transferred into a vessel charged
with ZrCp2Cl2 (25.8 mg, 0.1 mmol) and Mn powder (11 mg, 0.20
mmol). Next, 5-(bromomethyl)-2-phenyloxazole (2a) (47.6 mg, 0.20
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2018, 50, A–G

D
Z. Wang et al.
Special Topic
Synthesis
HO
CrCl2 (10 mol%), Proton Sponge (13 mol%)
L4 (13 mol%), NiCl2 (0.5 mol%)
DME, r.t.
R
OH
O
Cl
R1
+
N
R
H
N
CsI (1.0 equiv), Mn (2.0 equiv)
ZrCp2Cl2 (1.0 equiv), DME, –10 °C
N
Ts
R1
Ts
Ts
1
5
4
4g
Me
F
HO
HO
99:1 dr
94% ee
43% yield
99:1 dr
92% ee
50% yield
N
N
Ts
4a
4b
Ts
Me
Me
HO
HO
90:10 dr
92% ee
69% yield
99:1 dr
95% ee
55% yield
N
N
4d
4c
Ts
Ts
Me
HO
HO
Cl
Me
90:10 dr
93% ee
63% yield
99:1 dr
93% ee
63% yield
N
N
Ts
Ts 4e
4f
OH
N
99:1 dr
90% ee
63% yield
Ts
4g
Me
Scheme 4 Further substrate scope studies
mmol) and 3-phenylpropanal (13.2 mg, 0.10 mmol) were added in
succession. The resulting mixture was stirred at –10 °C for 24 h. After
full consumption of the aldehyde, the reaction mixture was diluted
with EtOAc and the resulting suspension was filtered through a pad of
silica gel using EtOAc as the eluent. The volatiles were evaporated in
vacuo. The residue was purified by column chromatography (EtO-
Ac/PE, 1:5) to give the desired product.
(R)-5-Chloro-1-[(R)-5-methylene-2-phenyl-4,5-dihydrooxazol-4-
yl]pentan-1-ol (3b)
20
Yield: 17.1 mg, 0.061 mmol (61%); colorless oil; [α]D +33.9 (c 0.55,
CH2Cl2).
IR (neat): 3367, 2925, 1450, 1327, 1084, 926, 825, 693 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 7.97–7.95 (d, J = 8 Hz, 2 H), 7.53–7.41
(m, 3 H), 4.94–4.92(m, 1 H), 4.78–4.76 (m, 1 H), 4.41–4.39 (m, 1 H),
3.76–3.74 (m, 1 H), 3.53 (t, J = 6 Hz, 2 H), 1.80–1.52 (m, 6 H).
13C NMR (100 MHz, CDCl3): δ = 163.6, 159.2, 132.2, 128.7, 128.3,
126.4, 86.5, 73.7, 73.3, 45.0, 32.5, 31.2, 23.5.
20
Yield: 16.6 mg, 0.057 mmol (57%); colorless oil; [α]D +30.9 (c 0.38,
CH2Cl2).
IR (neat): 3306, 2924, 1647, 1260, 1083, 925, 799, 693 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 7.92 (d, J = 8 Hz, 2 H), 7.49–7.37 (m, 3
H), 7.27–7.13 (m, 5 H), 4.90–4.89 (m, 1 H), 4.76–4.75 (m, 1 H), 4.35–
4.34 (m, 1 H), 3.78–3.74 (m, 1 H), 2.94–2.87 (m, 1 H), 2.73–2.65 (m, 1
H), 1.89–1.79 (m, 2 H).
HRMS (ESI+): m/z [M + 1]+ calcd for C15H18ClNO2: 280.1104; found:
280.1098.
HPLC: Chiralcel OD-H column, hexanes/i-PrOH (90:10), 1.0 mL/min,
210 nm; tR (minor) = 5.5 min, tR (major) = 7.3 min; 94% ee.
13C NMR (100 MHz, CDCl3): δ = 163.5, 159.1, 141.8, 132.2, 128.7,
128.6, 128.5, 128.3, 126.7, 126.0, 86.6, 73.4, 73.0, 33.6, 32.3.
HRMS (ESI+): m/z [M + 1]+ calcd for C19H19NO2: 294.1494; found:
294.1484.
(1R)-3,7-Dimethyl-1-[(R)-5-methylene-2-phenyl-4,5-dihydrooxaz-
ol-4-yl]oct-6-en-1-ol (3c)
Yield: 17.2 mg, 0.055 mmol (51%); colorless liquid; [α]D20 +65.3 (c 1.7,
CH2Cl2).
HPLC: Chiralcel OD-H column, hexanes/i-PrOH (98:2), 1.0 mL/min,
210 nm; tR (minor) = 13.1 min, tR (major) = 16.3 min; 95% ee.
IR (neat): 3411, 2961, 1451, 927, 779, 693 cm–1
.
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2018, 50, A–G

E
Z. Wang et al.
Special Topic
Synthesis
1H NMR (400 MHz, CDCl3): δ = 7.97 (d, J = 8 Hz, 2 H), 7.52–7.40 (m, 3
H), 5.09–5.05 (m, 1 H), 4.92 (s, 1 H), 4.76 (d, J = 4 Hz, 1 H), 4.38 (s, 1 H),
3.92–3.83 (m, 1 H), 2.00–1.23 (m, 13 H), 0.95–0.90 (m, 3 H).
(R)-1-[(R)-2-(2-Bromophenyl)-5-methylene-4,5-dihydrooxazol-4-
yl]hexan-1-ol (3g)
20
Yield: 22.0 mg, 0.065 mmol (65%); yellow oil; [α]D +47.2 (c 3.50,
13C NMR (100 MHz, CDCl3): δ = 163.42, 163.39, 159.3, 159.1, 132.1,
131.5, 131.4, 128.6, 128.3, 126.5, 124.8, 86.44, 86.37, 73.8, 73.5, 71.8,
71.6, 39.2, 39.1, 38.1, 36.3, 29.3, 28.9, 25.9, 25.7, 25.4, 20.6, 19.1, 17.8.
HRMS (ESI+): m/z [M + 1]+ calcd for C20H27NO2: 314.2120; found:
314.2113.
CH2Cl2).
IR (neat): 3388, 2956, 1651, 1378, 1211, 1090, 923, 800, 642 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 7.75–7.69 (m, 2 H), 7.41–7.32 (m, 2 H),
4.94–4.93 (m, 1 H), 4.85–4.83 (m, 1 H), 4.44–4.43 (m, 1 H), 3.84–3.81
(m, 1 H), 1.66–1.56 (m, 3 H), 1.43–1.25 (m, 5 H), 0.90 (t, J = 8 Hz, 3 H).
13C NMR (100 MHz, CDCl3): δ = 162.7, 158.8, 134.2, 132.4, 131.5,
128.6, 127.4, 122.1, 86.9, 73.8, 73.6, 31.89, 31.85, 25.7, 22.7, 14.2.
HPLC: Chiralcel OD-H column, hexanes/i-PrOH (90:10), 1.0 mL/min,
210 nm; tR (minor) = 3.7 min, tR (major) = 4.8 min; 95% ee.
HRMS (ESI+): m/z [M + 1]+ calcd for C16H20BrNO2: 338.0756; found:
338.0743.
(R)-1-[(R)-2-(4-Bromophenyl)-5-methylene-4,5-dihydrooxazol-4-
yl]-5-chloropentan-1-ol (3d)
HPLC: Chiralcel OD-H column, hexanes/i-PrOH (90:10), 1.0 mL/min,
210 nm; tR (minor) = 6.1 min, tR (major) = 7.1 min; 94% ee.
20
Yield: 21.6 mg, 0.06 mmol (60%); yellowish liquid; [α]D +24.2 (c
1.08, CH2Cl2).
IR (neat): 3266, 2923, 1592, 1487, 1261, 1079, 922, 835, 724, 668 cm–1
.
(R)-1-[(R)-2-(2-Bromophenyl)-5-methylene-4,5-dihydrooxazol-4-
yl]heptan-1-ol (3h)
1H NMR (400 MHz, CDCl3): δ = 7.83 (d, J = 8 Hz, 2 H), 7.58 (d, J = 12 Hz,
2 H), 4.95–4.94 (m, 1 H), 4.76–4.75 (m, 1 H), 4.44–4.43 (m, 1 H), 3.78–
3.74 (m, 1 H), 3.55 (t, J = 8 Hz, 2 H), 1.85–1.51 (m, 6 H).
13C NMR (100 MHz, CDCl3): δ = 162.8, 158.9, 132.0, 129.8, 127.0,
125.3, 86.9, 73.5, 73.3, 45.0, 32.5, 31.3, 23.4.
20
Yield: 20.1 mg, 0.057 mmol (57%); colorless oil; [α]D +62.5 (c 2.00,
CH2Cl2).
IR (neat): 3346, 2962, 2926, 1654, 1313, 1260, 871, 799, 687 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 7.74–7.67 (m, 2 H), 7.41–7.32 (m, 2 H),
4.94–4.93 (m, 1 H), 4.84–4.83 (m, 1 H), 4.44–4.43 (m, 1 H), 3.84–3.81
(m, 1 H), 1.65–1.55 (m, 3 H), 1.41–1.25 (m, 7 H), 0.89 (t, J = 6 Hz, 3 H).
HRMS (ESI+): m/z [M + 1]+ calcd for C15H17BrClNO2: 358.0209; found:
358.0203.
13C NMR (100 MHz, CDCl3): δ = 162.7, 158.8, 134.2, 132.4, 131.5,
128.5, 127.4, 122.0, 86.9, 73.8, 73.6, 31.92, 31.89, 29.3, 25.6, 22.8,
14.2.
HPLC: Chiralcel OD-H column, hexanes/i-PrOH (90:10), 1.0 mL/min,
210 nm; tR (minor) = 5.9 min, tR (major) = 7.0 min; 95% ee.
(R)-1-[(R)-2-(4-Bromophenyl)-5-methylene-4,5-dihydrooxazol-4-
yl]hexan-1-ol (3e)
HRMS (ESI+): m/z [M + 1]+ calcd for C17H22BrNO2: 352.0912; found:
352.0901.
20
Yield: 15.3 mg, 0.045 mmol (45%); colorless oil; [α]D +22.2 (c 0.76,
HPLC: Chiralcel OD-H column, hexanes/i-PrOH (90:10), 1.0 mL/min,
210 nm; tR (minor) = 6.1 min, tR (major) = 7.1 min; 94% ee.
CH2Cl2).
IR (neat): 3325, 2922, 1645, 1261, 1175, 919, 832, 724, 669 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 7.84 (d, J = 8 Hz, 2 H), 7.58 (d, J = 4 Hz,
2 H), 4.94–4.93 (m, 1 H), 4.77–4.74 (m, 1 H), 4.43–4.42 (m, 1 H), 3.80–
3.74 (m, 1 H), 1.62–1.30 (m, 8 H), 0.89 (t, J = 6 Hz, 3 H).
(R)-1-[(R)-2-(2-Fluorophenyl)-5-methylene-4,5-dihydrooxazol-4-
yl]heptan-1-ol (3i)
20
Yield: 14.6 mg, 0.05 mmol (50%); yellow oil; [α]D +26.3 (c 1.70,
13C NMR (100 MHz, CDCl3): δ = 162.7, 158.9, 131.9, 129.8, 126.9,
CH2Cl2).
IR (neat): 3369, 2928, 1614, 1260, 1030, 801, 702, 658 cm–1
.
125.4, 86.8, 73.6, 73.3, 31.9, 31.8, 25.7, 22.7, 14.2.
HRMS (ESI+): m/z [M + 1]+ calcd for C16H20BrNO2: 338.0756; found:
338.0748.
1H NMR (400 MHz, CDCl3): δ = 7.89–7.86 (m, 1 H), 7.50–7.45 (m, 1 H),
7.24–7.12 (m, 2 H), 4.93–4.92 (m, 1 H), 4.82–4.81 (m, 1 H), 4.41–4.40
(m, 1 H), 3.82–3.79 (m, 1 H), 1.58–1.26 (m, 10 H), 0.85 (t, J = 6 Hz, 3
H).
HPLC: Chiralcel OD-H column, hexanes/i-PrOH (90:10), 1.0 mL/min,
210 nm; tR (minor) = 4.3 min, tR (major) = 5.0 min; 93% ee.
13C NMR (100 MHz, CDCl3): δ = 161.4 (d, JCF = 258.0 Hz, CF), 160.2 (d,
JCF = 6 Hz, C=N), 158.4, 133.7 (d, JCF = 9 Hz, Ph), 131.0, 124.2 (d, JCF = 4
Hz, Ph), 117.0 (d, JCF = 22 Hz, Ph), 115.2 (d, JCF = 9 Hz, Ph), 86.8, 73.6,
31.9, 31.8, 29.3, 26.0, 22.7, 14.2.
(R)-1-[(R)-2-(2-Bromophenyl)-5-methylene-4,5-dihydrooxazol-4-
yl]-5-chloropentan-1-ol (3f)
20
Yield: 25.1 mg, 0.07 mmol (70%); yellow liquid; [α]D +60.6 (c 2.28,
HRMS (ESI+): m/z [M + 1]+ calcd for C17H22FNO2: 292.1713; found:
CH2Cl2).
IR (neat): 2963, 1651, 1432, 1311, 1025, 865, 799, 700 cm–1
.
292.1706.
1H NMR (400 MHz, CDCl3): δ = 7.72–7.66 (m, 2 H), 7.39–7.30 (m, 2 H),
4.92–4.91 (m, 1 H), 4.82–4.81 (m, 1 H), 4.42–4.41 (m, 1 H), 3.79–3.73
(m, 1 H), 3.53 (t, J = 8 Hz, 2 H), 1.80–1.53 (m, 6 H).
HPLC: Chiralcel OD-H column, hexanes/i-PrOH (90:10), 1.0 mL/min,
210 nm; tR (minor) = 5.4 min, tR (major) = 6.1 min; 94% ee.
(S)-[(S)-2-Methylene-1-tosylindolin-3-yl](phenyl)methanol (4a);
Typical Procedure
13C NMR (100 MHz, CDCl3): δ = 162.7, 158.8, 134.2, 132.4, 131.5,
128.4, 127.4, 122.0, 87.0, 73.7, 73.5, 45.0, 32.5, 31.2, 23.4.
In a glovebox, to a mixture of anhydrous CrCl2 (1.2 mg, 0.01 mmol),
1,8-bis[(S)-4-ethyl-4,5-dihydrooxazol-2-yl]-9H-carbazole (L4) (4.6
mg, 0.013 mmol,) and Proton Sponge (2.8 mg, 0.013 mmol) was add-
ed DME (0.2 mL) under a nitrogen atmosphere. The mixture was
stirred vigorously at r.t. for 2 h before being transferred into a vessel
charged with CsI (26.6 mg, 0.1 mmol), NiCl2 (0.05 mg), ZrCp2Cl2 (25.8
HRMS (ESI+): m/z [M + 1]+ calcd for C15H17BrClNO2: 358.0209; found:
358.0196.
HPLC: Chiralcel OD-H column, hexanes/i-PrOH (90:10), 1.0 mL/min,
210 nm; tR (minor) = 8.6 min, tR (major) = 10.9 min; 94% ee.
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2018, 50, A–G

F
Z. Wang et al.
Special Topic
Synthesis
mg, 0.1 mmol) and Mn powder (11 mg, 0.20 mmol). Next, 2-(chloro-
methyl)-1-tosyl-1H-indole (5a) (63.8 mg, 0.20 mmol) and 3-phenyl-
propanal (13.2 mg, 0.10 mmol) were added in succession. The result-
ing mixture was stirred at –10 °C for 24 h. After full consumption of
the aldehyde, the reaction mixture was diluted with EtOAc and the re-
sulting suspension was filtered through a pad of silica gel using EtOAc
as the eluent. The volatiles were evaporated in vacuo. The residue was
purified by column chromatography (EtOAc/PE, 1:5) to give the de-
sired product.
HPLC: Chiralcel OD-H column, hexanes/i-PrOH (95:5), 1.0 mL/min,
210 nm; tR (minor) = 22.3 min, tR (major) = 26.3 min; 92% ee.
(R,E)-1-[(S)-2-Methylene-1-tosylindolin-3-yl]-3-(o-tolyl)prop-2-
en-1-ol (4d)
Yield: 24.0 mg, 0.056 mmol (55%); yellowish oil; [α]D20 +67.1 (c 2.40,
CH2Cl2).
IR (neat): 3544, 2969, 1600, 1165, 952, 703, 657 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 7.82 (d, J = 8 Hz, 1 H), 7.61 (d, J = 8 Hz,
2 H), 7.25–7.28 (m, 2 H), 7.22–7.03 (m, 7 H), 6.42 (d, J = 8 Hz, 1 H),
5.75–5.69 (m, 2 H), 4.84 (s, 1 H), 3.81 (d, J = 8 Hz, 1 H), 3.74 (d, J = 8 Hz,
1 H), 2.29 (s, 3 H), 2.16 (s, 3 H).
13C NMR (100 MHz, CDCl3): δ = 145.3, 144.7, 142.6, 135.6, 135.58,
134.7, 131.2, 130.3, 129.5, 129.2, 128.9, 128.7, 127.8, 127.3, 126.2,
125.93, 125.91, 124.2, 115.6, 99.0, 76.0, 52.4, 21.7, 19.7.
20
Yield: 16.8 mg, 0.043 mmol (43%); yellow oil; [α]D +113.7 (c 0.83,
CH2Cl2).
IR (neat): 3544, 3064, 1956, 1653, 1599, 1241, 1092, 948, 810, 700
cm–1
.
1H NMR (400 MHz, CDCl3): δ = 7.80 (d, J = 8 Hz, 1 H), 7.65 (d, J = 8 Hz,
2 H), 7.30–7.20 (m, 7 H), 6.92 (d, J = 8 Hz, 2 H), 6.84–6.80 (m, 1 H),
5.77 (s, 1 H), 4.89 (s, 1 H), 3.74 (d, J = 8 Hz, 1 H), 3.28 (d, J = 8 Hz, 1 H),
2.38 (s, 3 H).
13C NMR (101 MHz, CDCl3): δ = 145.9, 144.9, 142.5, 139.9, 134.8,
129.6, 129.1, 128.7, 128.4, 128.3, 127.5, 127.4, 125.9, 124.2, 116.4,
101.8, 76.3, 54.2, 21.8.
HRMS (EI+): m/z [M]+ calcd for C26H25NO3S: 431.1555; found:
431.1444.
HPLC: Chiralcel OD-H column, hexanes/i-PrOH (95:5), 1.0 mL/min,
210 nm; tR (minor) = 74.2 min, tR (major) = 84.7 min; 95% ee.
HRMS (EI+): m/z [M]+ calcd for C23H21NO3S: 391.1242; found:
391.1132.
(R,E)-1-[(S)-2-Methylene-1-tosylindolin-3-yl]hex-2-en-1-ol (4e)
20
Yield: 24.2 mg, 0.063 mmol (63%); colorless oil; [α]D +82.7 (c 1.60,
HPLC: Chiralcel OD-H column, hexanes/i-PrOH (98:2), 1.0 mL/min,
210 nm; tR (minor) = 7.3 min, tR (major) = 7.7 min; 94% ee.
CH2Cl2).
IR (neat): 3541, 2960, 1599, 1165, 960, 862, 808, 751, 657 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 7.80 (d, J = 8 Hz, 1 H), 7.62 (d, J = 8 Hz,
2 H), 7.24 (t, J = 8 Hz, 1 H), 7.18 (t, J = 8 Hz, 3 H), 7.01 (t, J = 8 Hz, 1 H),
5.69 (s, 1 H), 5.35–5.28 (m, 1 H), 5.13–5.08 (m, 1 H), 4.78 (s, 1 H), 3.64
(d, J = 8 Hz, 1 H), 3.43–3.40 (m, 1 H), 2.34 (s, 3 H), 1.87–1.80 (m, 2 H),
1.28–1.23 (m, 2 H), 0.79 (t, J = 8 Hz, 3 H).
13C NMR (100 MHz, CDCl3): δ = 145.5, 144.7, 142.6, 135.2, 134.9,
129.6, 128.6, 127.9, 127.4, 125.9, 124.2, 115.7, 99.1, 75.7, 52.3, 34.3,
22.3, 21.7, 13.8.
(S)-(3-Fluorophenyl)[(S)-2-methylene-1-tosylindolin-3-yl]metha-
nol (4b)
20
Yield: 20.5 mg, 0.05 mmol (50%); yellowish oil; [α]D +75.5 (c 2.10,
CH2Cl2).
IR (neat): 3533, 2970, 1653, 1164, 1032, 948, 877, 701, 656 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 7.78 (d, J = 8 Hz, 1 H), 7.62 (d, J = 8 Hz,
2 H), 7.24–7.16 (m, 4 H), 6.94 (t, J = 8 Hz, 1 H), 6.87–6.83 (m, 1 H),
6.68–6.62 (m, 2 H), 6.26 (d, J = 8 Hz, 1 H), 5.72 (s, 1 H), 4.78 (s, 1 H),
3.71 (d, J = 8 Hz, 1 H), 3.43 (d, J = 8 Hz, 1 H), 2.36 (s, 3 H).
13C NMR (100 MHz, CDCl3): δ = 161.8 (d, JCF = 250.0 Hz, CF), 145.4 (d,
JCF = 8 Hz, Ph), 145.0, 142.6, 134.7, 129.7 (d, JCF = 9 Hz, Ph), 128.9,
127.4, 125.7, 124.3, 123.1, 123.06, 116.3, 115.3 (d, JCF = 21 Hz, Ph),
115.1, 114.5, 114.2 (d, JCF = 22 Hz, Ph), 101.5, 75.8, 54.0, 21.7.
HRMS (ESI+): m/z [M + 1]+ calcd for C22H25NO3S: 384.1633; found:
384.1629.
HPLC: Chiralcel OD-H column, hexanes/i-PrOH (98:2), 1.0 mL/min,
210 nm; tR (minor) = 20.7 min, tR (major) = 22.4 min; 93% ee.
(R,E)-1-((S)-5-chloro-2-methylene-1-tosylindolin-3-yl)hex-2-en-
1-ol (4f)
Yield: 63 %; yellowish oil; [α]D20 = 57.2539 (c = 3.6, CH2Cl2).
IR (neat) cm–1: 3547.1, 2963.9, 1652.3, 1090.03, 957.7, 865.3, 713.8,
HRMS (EI+): m/z [M]+ calcd for C23H20FNO3S: 409.1148; found:
409.1112.
HPLC: Chiralcel OD-H column, hexanes/i-PrOH (98:2), 1.0 mL/min,
210 nm; tR (minor) = 61.5 min, tR (major) = 67.1 min; 92% ee.
1H NMR (400 MHz, CDCl3): δ = 7.74 (d, J = 8 Hz, 1H), 7.61 (d, J = 8 Hz,
1H), 7.23–7.20 (m, 4H), 5.70 (s, 1H), 5.38–5.33 (m, 1H), 5.08–5.03 (m,
1H), 4.79 (s, 1H), 3.66 (d, J = 4 Hz, 1H), 3.51 (t, J = 6 Hz, 1H), 2.37 (s,
3H), 1.86–1.82 (m, 2H), 1.29–1.23 (m, 2H), 0.81 (t, J = 6 Hz, 3H).
13C NMR (100 MHz, CDCl3): δ = 145.1, 145.05, 141.1, 135.7, 134.5,
131.4, 129.7, 129.5, 128.5, 127.5, 127.4, 126.1, 116.6, 99.2, 75.8, 51.8,
34.4, 22.3, 21.7, 13.7.
(S)-[(S)-2-Methylene-1-tosylindolin-3-yl](o-tolyl)methanol (4c)
Yield: 28.0 mg, 0.069 mmol (69%); yellowish oil; [α]D20 +114.1 (c 5.60,
CH2Cl2).
IR (neat): 3545, 2967, 1599, 1166, 949, 699, 659 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 7.81 (d, J = 8 Hz, 1 H), 7.71 (d, J = 8 Hz,
2 H), 7.37 (d, J = 8 Hz,1 H), 7.26–7.15 (m, 6 H), 6.95 (d, J = 8 Hz, 1 H),
6.74 (t, J = 8 Hz, 1 H), 5.84 (s, 1 H), 5.03 (s, 1 H), 3.67 (d, J = 8 Hz, 1 H),
3.55 (d, J = 8 Hz, 1 H), 2.35 (s, 3 H), 1.32 (s, 3 H).
HRMS (ESI+): cald for C22H24ClNO3S: 417.1165; found: 417.1129.
i
HPLC: Chiralcel OD-H column, hexanes: PrOH = 98:2, 1.0 mL/min,
210 nm; tR (minor) = 22.8 min, tR (major) = 24.5 min, 93% ee.
13C NMR (100 MHz, CDCl3): δ = 146.1, 144.9, 142.4, 138.5, 136.0,
134.9, 130.0, 129.7, 128.7, 128.66, 128.1, 127.3, 126.7, 126.5, 125.3,
124.2, 116.2, 102.3, 71.2, 54.4, 21.7, 19.0.
HRMS (EI+): m/z [M]+ calcd for C24H23NO3S: 405.1399; found:
405.1287.
(R,E)-1-[(R)-3-Methylene-1-tosylindolin-2-yl]hex-2-en-1-ol (4g)
Yield: 24.2 mg, 0.063 mmol (63%); yellowish oil; [α]D20 +47.1 (c 2.23,
CH2Cl2).
IR (neat): 3511, 2958, 1644, 1460, 1165, 1031, 973, 760, 700 cm–1
.
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2018, 50, A–G

G
Z. Wang et al.
Special Topic
Synthesis
1H NMR (400 MHz, CDCl3): δ = 7.75 (d, J = 8 Hz,1 H), 7.51 (d, J = 8 Hz, 2
H), 7.27 (d, J = 8 Hz, 2 H), 7.15 (d, J = 8 Hz, 2 H), 7.06 (t, J = 6 Hz, 1 H),
5.73–5.66 (m, 1 H), 5.43–5.42 (m, 1 H), 5.37–5.32 (m, 1 H), 4.96 (s, 1
H), 4.72–4.71 (m, 1 H), 4.27 (s, 1 H), 2.33 (s, 3 H), 1.88–1.82 (m, 2 H),
1.21–1.13 (m, 2 H), 0.70 (t, J = 8 Hz, 3 H).
13C NMR (100 MHz, CDCl3): δ = 144.6, 144.0, 142.0, 134.2, 133.7,
130.8, 130.2, 129.8, 127.3, 126.3, 125.1, 120.8, 117.3, 104.9, 77.3, 71.2,
34.3, 22.1, 21.7, 13.5.
(3) Hummel, J. R.; Boerth, J. A.; Ellman, J. A. Chem. Rev. 2017, 117,
9163.
(4) (a) Zhuo, C.-X.; Zhang, W.; You, S.-L. Angew. Chem. Int. Ed. 2012,
51, 12662. (b) Wang, D.-S.; Chen, Q.-A.; Lu, S.-M.; Zhou, Y.-G.
Chem. Rev. 2012, 112, 2557. (c) Zhuo, C.-X.; Zheng, C.; You, S.-L.
Acc. Chem. Res. 2014, 47, 2558. (d) Yang, Z.-P.; Zheng, C.; Huang,
L.; Qian, C.; You, S.-L. Angew. Chem. Int. Ed. 2017, 56, 1530.
(5) (a) Yang, Z.-P.; Wu, Q.-F.; Shao, W.; You, S.-L. J. Am. Chem. Soc.
2015, 137, 15899. (b) Zheng, C.; You, S.-L. Chem 2016, 1, 830.
(c) Wang, Y.; Zheng, C.; You, S.-L. Angew. Chem. Int. Ed. 2017, 56,
15093.
HPLC: Chiralcel OD-H column, hexanes/i-PrOH (90:10), 1.0 mL/min,
210 nm; tR (minor) = 15.6 min, tR (major) = 17.5 min; 90% ee.
(6) (a) Bao, M.; Nakamura, H.; Yamamoto, Y. J. Am. Chem. Soc. 2001,
123, 759. (b) Peng, B.; Zhang, S.; Yu, X.; Feng, X.; Bao, M. Org.
Lett. 2011, 13, 5402.
Funding Information
(7) (a) Tian, Q.; Bai, J.; Chen, B.; Zhang, G. Org. Lett. 2016, 18, 1828.
(b) Chen, W.; Bai, J.; Zhang, G. Adv. Synth. Catal. 2017, 359, 1227.
(8) (a) Chen, W.; Yang, Q.; Zhou, T.; Tian, Q.; Zhang, G. Org. Lett.
2015, 17, 5236. (b) Xiong, Y.; Zhang, G. Org. Lett. 2016, 18, 5094.
(c) Tian, Q.; Zhang, G. Synthesis 2016, 48, 4038. (d) Guo, R.; Yang,
Q.; Tian, Q.; Zhang, G. Sci. Rep. 2017, 7, 4873. (e) Ji, H.; Tian, Q.;
Xiang, J.; Zhang, G. Chin. Chem. Lett. 2017, 28, 1182. (f) Xiong, Y.;
Zhang, G. J. Am. Chem. Soc. 2018, 140, 2735.
We are grateful to NSFC-21772218, 21421091, XDB20000000, the
‘Thousand Plan’ Youth program, State Key Laboratory of Organome-
tallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese
Academy of Sciences, the Science and Technology Innovative Research
Team in Higher Educational Institutions of Hunan Province (2012-
318) and the Construct Program of the Key Discipline in Hunan Prov-
ince.
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1)
(9) For selected examples of Nozaki–Hiyama–Kishi reactions, see:
(a) Okude, Y.; Hirano, S.; Hiyama, T.; Nozaki, H. J. Am. Chem. Soc.
1977, 99, 3179. (b) Jin, H.-L.; Uenishi, J.-I.; Christ, W. J.; Kishi, Y.
J. Am. Chem. Soc. 1986, 108, 5644. (c) Takai, K.; Tagashira, M.;
Kuroda, T.; Oshima, K.; Utimoto, K.; Nozaki, H. J. Am. Chem. Soc.
1986, 108, 6048. (d) Fürstner, A. Chem. Rev. 1999, 99, 991.
(e) Inoue, M.; Suzuki, T.; Nakada, M. J. Am. Chem. Soc. 2003, 125,
1140. (f) Xia, G.-Y.; Yamamoto, H. J. Am. Chem. Soc. 2007, 129,
496. (g) Kim, D.; Dong, C.-G.; Kim, J. T.; Guo, H.-B.; Huang, J.;
Tiseni, P. S.; Kishi, Y. J. Am. Chem. Soc. 2009, 131, 15636.
(h) Harper, K. C.; Sigman, M. S. Science 2011, 333, 1875. (i) Deng,
Q.-H.; Wadepohl, H.; Gade, L. H. Chem. Eur. J. 2011, 17, 14922.
(j) Gil, A.; Albericio, F.; Alvarez, M. Chem. Rev. 2017, 117, 8420.
(k) Yahata, K.; Ye, N.; Iso, K.; Ai, Y.; Lee, J.; Kishi, Y. J. Org. Chem.
2017, 87, 8808. (l) Yahata, K.; Ye, N.; Iso, K.; Naini, S.; Yamashita,
S.; Ai, Y.; Kishi, Y. J. Org. Chem. 2017, 87, 8792. (m) Yahata, K.;
Ye, N.; Ai, Y.; Iso, K.; Kishi, Y. Angew. Chem. Int. Ed. 2017, 56,
10796.
Acknowledgment
We thank Mr. Bin Chen for preparing the chiral ligands.
Supporting Information
Supporting information for this article is available online at
https://doi.org/10.1055/s-0037-1609753.
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© Georg Thieme Verlag Stuttgart · New York — Synthesis 2018, 50, A–G